Across Colorado, Nebraska and Wyoming, authorities shut down treacherous interstates coated in ice and snow.

The National Weather Service warned anyone on the road to pack a survival kit.

Some places have had as much as four feet of snow. At Denver's airport, United Airlines cancelled about half of its 400 flights.

Forecasters expect the powerful storm to pack even more snow and high winds as it heads east.

"It's going to move out onto the eastern plains. Northeast of Colorado will have near blizzard like conditions. Farther east the same storm is causing severe thunderstorms and tornadoes and over the southern plains," Mike Nelson, chief meteorologist with KMGH-TV, said.